Clutch protection system

Abstract

A clutch protection system to guard against overheating due to excessive slippage in a friction clutch (12). The system which is particularly suitable for use with a tractor power take-off clutch includes sensors (18, 19) to provide signals indicative of the input and output speeds of the clutch and an indicating device (56) which receives a first signal (I) indicative of the clutch input speed and a second signal (X) indicative of either the clutch output speed when the clutch engagement pressure is applied or the clutch input speed when the clutch engagement pressure is not applied. The indicating device has a signal level indicative of the difference between the first and second signals minus a signal indicative of the cooling effect on the clutch due to its own rotation. A comparator (56) compares the signal level of the indicating device with a predetermined signal level indicative of, for example, a potentially damaging clutch operating condition and actuates a warning device (40) and disengages the clutch when the predetermined clutch operating condition occurs.

I claim: 
     
       1. A clutch protection system to guard against overheating due to excessive slippage in a friction clutch (12) having an engagement means which applies an engagement pressure to the clutch, the system being characterised by the inclusion of sensing means (18,19) to provide signals indicative of the input and output speeds of the clutch; an indicating device (56) which receives a first signal (I) indicative of the clutch input speed and a second signal (X) indicative of either the clutch output speed when the clutch engagement pressure is applied or the clutch input speed when the clutch engagement pressure is not applied, the indicating device having a signal level indicative of the difference between the first and second signals minus a signal indicative of the cooling effect on the clutch due to its own rotation; comparison means (56) for comparing the signal level of the indicating device with a predetermined signal level indicative of a clutch operating condition; and response means responsive to a predetermined comparison result to actuate a warning device (40). 
     
     
       2. A clutch protection system according to claim 1 for use with a friction clutch (12) in which the engagement means comprises a fluid pressure operated clutch actuator (12a) fed with pressurised fluid via a solenoid operated valve (14) which is oscillated at high frequency between "off" and "on" conditions during clutch engagement to control the rate of build up of pressure in the actuator using a pulse width modulation technique, the system being characterised in that the second signal (X) received by the indicating device (56) is taken as the clutch output speed signal during the "on" condition of the solenoid operated valve and as the clutch input speed signal during the "off" condition of said valve. 
     
     
       3. A clutch protection system according to claim 1 characterised in that the comparison means (56) compares the signal level of the indicating device (56) with first and second predetermined signal levels indicative of different levels of clutch slippage and the response means actions a warning (40) if the signal level of the indicating device exceeds the first predetermined signal level and actions a further warning and disengages (60) the clutch (12) if the signal level of the indicating device (56) exceeds the second predetermined signal level. 
     
     
       4. A clutch protection system according to claim 1 characterised in that the indicating device signal level used to action disengagement of the clutch is set at the signal level reached by the indicating device (56) in two seconds with the clutch (12) fully engaged and with the clutch input (16) running at 2200 revs/min and the clutch output (17) held stationary. 
     
     
       5. A clutch protection system according to claim 1 characterised in that the signal (S) indicative of the cooling effect of the clutch (12) due to its own rotation is set at a level such that it will reduce the counter signal level from the clutch disengagement level to zero in three minutes with a clutch input speed of 1800 rev/min and no clutch slippage. 
     
     
       6. A tractor power take-off drive including a friction clutch (12) having a protection system according to claim 1. 
     
     
       7. A clutch protection system according to claim 1 characterised in that the response means disengages the clutch in response to a predetermined comparison result. 
     
     
       8. A clutch protection system according to claim 1 characterised in that the indicating device comprises a digital counter (56) which receives a first series of count pulses (I) indicative of clutch input speed and a second series of count pulses (X) which is indicative of either the clutch output speed when the clutch engagement pressure is applied or the clutch input speed when the clutch engagement pressure is not applied, the arrangement being such that the count level in the counter represents the first series of count pulses minus the product of the second series of count pulses and a scaling factor (S) which simulates said cooling effect. 
     
     
       9. A clutch protection system to guard against overheating due to excessive slippage in a friction clutch (12) having an engagement means which applies an engagement pressure to the clutch, the system being characterised by the inclusion of sensing means (18,19) to provide signals indicative of the input and output speeds of the clutch; an indicating device (56) which receives a first signal (I) indicative of the clutch input speed and a second signal (X) indicative of either the clutch output speed when the clutch engagement pressure is applied or the clutch input speed when the clutch engagement pressure is not applied, the indicating device having a signal level which represents the first signal minus the product of the second signal and a scaling factor (S) which simulates the cooling effect on the clutch due to its own rotation; comparison means (56) for comparing the signal level of the indicating device with a predetermined signal level indicative of a clutch operating condition; and response means responsive to a predetermined comparison result to actuate a warning device (40).